If you have your Drivers Information Console set to "Enhanced" mode there should be a power meter on the right side of the speedometer that has a bar that grows up when you're using power and grows down when you're doing regenerative braking. When the car is unable to accept full regen, you'll see a thin white horizontal line below the centre point of that power meter - it indicates the maximum regen that the car can use. If you fully charge the battery to 100% that line will be very close to the "0" point on the meter, and it will gradually move down until it disappears off the bottom when you've used up around 3kWh or so of energy.